The reason seems to be, or related to, the capture sharpening module.
I have a really strange motive all over the image when I open your image+pp3 in the appimage (stable, 5.8) and zoom to 100%. It disappears when I turn the capture sharpening off and then on again. It does not return if I now stop-start RawTherapee with this image.
When using the latest development (5.8-2780-g3b39ff384) I see the black blotches/squares (about the same as can be seen in your above image). Same thing happens when I turn on/off capture sharpening: Blotch is gone afterwards, does not return.
Here’s a screenshot of the motive I’m seeing in the stable, appimage version:
thanks for checking it out! in my case I have to turn off both capture sharpening and aberration correction in order for them to go away. previous version works fine
That would actually explain it, since you don’t even need to turn reconstruction off, you just have to switch it to Blend for the black blotches to go away.
Well, let’s Alberto have a look first. If things are not problematic in ART, then we might as well revert. But if things can be fixed, there may be a very nice improvement to the reconstruction.
This change followed a discussion on Darktable in january, and Alberto @agriggio made proposals to improve HR. They have been tested by ART users, and by myself. The improvement is significant.
But, it leads to a slowdown and in some cases to bad behaviour.
Considering the positive opinions, I didn’t go through the “issue” stage of RT, it’s a mistake? but who doesn’t make mistakes?